I wouldn't classify Megadrive as a shemups console. Megardive was the favourite console for coin op conversions. It had everything, platforms, beat em ups, shoot em ups etc. And don't forget that Sega had Sonic as a mascot, a character appearing in platform games. If you want to speak about the absolute console for shoot em ups, then this is the Saturn.

I used my Mega Drive nearly only for platformers. A pity I couldn't find phantasy star titles here at that time but after all I agree it was a mixed console, could do anything well enough.